1. Field of the Invention
This invention is related generally to a method for capturing an image, and more particularly to a method for capturing image which avoids an overexposure phenomenon.
2. Description of Related Art
In photography, an exposure operation is typically performed through an auto exposure function to achieve the ideal brightness for an entire image. When under insufficient ambient lighting or when the exposure time is below a safe shutter speed, a flash lamp is employed for brightness compensation so that the captured image does not become unrecognizable due to inadequate brightness.
Generally speaking, an intensity of a main flash is estimated in accordance with a pre-flash image. In order to increase the accuracy of estimating the main flash intensity when shooting at close range, a conventional method follows the steps outlined hereafter. When a user switches to a proximity mode, a digital camera decreases a pre-flash intensity so that the estimation of the main flash is accurate. Alternatively, the digital camera determines whether it is shooting in proximity mode according to an auto focus data, so as to limit a light entrance amount by switching diaphragms, and thereby accurately estimate the main flash intensity. The digital camera may also estimate the main flash intensity at proximity through a second pre-flash.
However, if the user has not switched to the proximity mode when shooting images at close range, inaccurate estimations of the main flash usually occur and overexposed images are obtained. Moreover, when the auto focus estimation is inaccurate, the time points for switching the diaphragms may be incorrect. Thus, for an object at far range for example, inaccurate estimation of the main flash results and a dark corner problem is generated. On the other hand, although the overexposure problem at close range may be alleviated by firing the pre-flash twice at a same time, when the intensity of the second pre-flash is too low, the flash lamp becomes unstable, and when the intensity of the second pre-flash is too high, a voltage of the main flash becomes too low and the main flash fails to fire.